This invention relates to multiplex communication system technology and relates to a circuit switching method for multiplex communication equipment where multiple communication channels are used by switching, and in particular, relates to a circuit switching control method for multiplex communication equipment where switching is made between an active circuit and a spare circuit.
There is a known method to transfer data by connecting two pieces of data terminal equipment (hereinafter called "DTE") using a high speed digital circuit and a method to transfer voice information by connecting two pieces of voice terminal equipment, such as telephones or facsimile equipment, using a high speed digital circuit.
In the former case, the two DTE's are constantly connected for data transfer, and both DTE's are connected by connection data.
In the latter case, communication is achieved by making a call connection based on dial information each time a call is made.
In the past, these two communication methods were not made on the same circuit because of the difference in connection method.
On the other hand, a multiplex communication system is being considered where a circuit is efficiently used by transferring data and voice information on the same high speed digital circuit.
The concept of such multiplex communication system is explained using FIG. 3. A multiplex communication system is constructed by connecting multiplex communication equipment 1, accommodating multiple pieces of DTE 2 and multiple pieces of voice terminal equipment 3, and multiplex communication equipment 1', accommodating multiple pieces of DTE2' and multiple pieces of voice terminal equipment 3', via a high speed digital circuit 4.
The transmitting side DTE 2 and the receiving side DTE 2', where data transfer is made constantly, are fixedly connected in advance between each other using a certain channel (CH1-CH3) of high speed digital circuit 4. Such fixed connection is achieved by securing a band for fixed connection within high speed digital circuit 4 on a priority basis.
A communication between a calling side voice terminal equipment 3 and a receiving side voice terminal equipment 3', which could take place at any time, is achieved by using one of the necessary channels (CH4-CH6) of the high speed digital circuit 4, and a call connection is made by using a control or Dp channel (DpCH).
For example, when a call is made from #100 voice terminal 3 to #201 voice terminal 3', multiplex communication equipment 1 captures an open channel (CH4) of circuit 4 based on the dial information to secure a transmission line to multiplex communication equipment 1', and then transfers call connection data, created based on the dial information, to multiplex communication equipment 1' via the Dp channel of circuit 4.
Multiplex communication equipment 1' on the receiving side accomplishes connection with #201 voice terminal equipment 3' based on the call connection data received via the Dp channel.
Next, when a call is from #102 voice terminal equipment 3 to #200 voice terminal equipment 3', multiplex communication equipment 1 captures an open channel (CH5) of circuit 4 based on the dial information to secure a transmission line to multiplex communication equipment 1', and then transfers call connection data, created based on the dial information, to multiplex communication equipment 1' via the Dp channel of circuit 4.
Multiplex communication equipment 1' on the receiving side accomplishes connection with #200 voice terminal equipment 3' based on the call connection data received via the Dp channel.
Next, when a call is made from #202 voice terminal equipment 3' to #101 voice terminal equipment 3, multiplex communication equipment 1' captures an open channel (Ch6) of circuit 4 based on the dial information to secure a transmission line to multiplex communication equipment 1, and then transfers call connection data, created based on the dial information, to multiplex communication equipment 1 via the Dp channel of circuit 4.
Multiplex communication equipment 1 on the receiving side accomplishes connection with #101 voice terminal equipment 3 based on the call connection data received via the Dp channel.
By providing such a structure, voice information can be transferred to the other voice terminal equipment dynamically, in other words on as required basis, while transferring data constantly, on the same circuit.
In such a multiplex communication system, it becomes necessary to have a spare circuit to enable continuation of transmission in case of circuit accident. For example, a circuit switching method is known whereby a spare circuit is connected at the same communication speed as the active circuit when switching from the active circuit to the spare circuit in a communication system having an active circuit and a spare circuit. Under this switching method, when the circuit switching control equipment connects to the spare circuit, the spare circuit requires connection at the same communication speed as the active circuit or at a communication speed covering the communication speed of the active circuit.
Under this switching method, even if there is some data with low necessity or a band normally not used in the active circuit, the total bandwidth of the private line, including those low usage rate items, will have to be secured in the spare circuit, resulting in a problem of wasteful cost incurred due to the unused band when a public network is used as the spare circuit.
As explained above, under the conventional circuit switching method, the usage rate of the switched circuit is low and so there will be a wasteful cost for using the circuit.